1. Field of the Invention
The present invention relates in general to power seat slide devices for motor vehicles or the like and more particularly to automotive power seat slide devices of a type which comprises two lower rails which are unmovably mounted on a vehicle floor, two upper rails which are slidably engaged with the lower rails and support thereon a seat, and an electric power device which moves the upper rails to a desired fore-and-aft position relative to the lower rails with an aid of electric power.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional power seat slide device of the above-mentioned type will be described with reference to FIG. 6 of the accompanying drawings.
The conventional power seat slide device generally comprises two rail units which are substantially the same in construction. As is understood from the drawing (viz., FIG. 6), each rail unit includes a lower rail 1 which is unmovably mounted on a vehicle floor "F", an upper rail 5 which is slidably engaged with the lower rail 1 and front and rear rollers 8a and 8b which are put between the lower and upper rails 1 and 5 to smooth the movement of the upper rail 5 relative to the lower rail 1. Although not shown in the drawing, a seat is mounted on the upper rails, so that movement of the upper rails 5 relative to the lower rails induces movement of the seat in the same direction relative to the vehicle floor "F".
Each lower rail 1 has first and second spaced front stoppers 2a and 2b and first and second spaced rear stoppers 2c and 2d secured thereto, and similar to this, each upper rail 5 has first and second spaced front stoppers 6a and 6b and first and second spaced rear stoppers 6c and 6d secured thereto. As shown, the front roller 8a is arranged to roll between the first front stopper 2a and the first rear stopper 2c and the rear roller 8b is arranged to roll between the second front stopper 2b and the second rear stopper 2d. When the upper rail 5 assumes its rearmost position as shown in the drawing, the first rear stopper 6c of the upper rail 5 presses the front roller 8a against the first rear stopper 2c of the lower rail 1 and at the same time, the second rear stopper 6d of the upper rail 5 presses the rear roller 8b against the second rear stopper 2d of the lower rail 1 thereby to achieve an assured stopping of the upper rail 5 at such extreme position. While, when the upper rail 5 assumes its frontmost position, the first front stopper 6a of the upper rail 5 presses the front roller 8a against the first front stopper 2a of the lower rail 1 and at the same time, the second front stopper 6b of the upper rail 5 presses the rear roller 8b against the second front stopper 2b of the lower rail 1.
However, due to inevitable dimensional error of constituent parts and inevitable assembly error, the two rail units of the above-mentioned conventional power seat slide device have failed to have a satisfied symmetrization therebetween, which causes a marked sway of the seat at the frontmost or rearmost position. Furthermore, marked shock has been produced when the seat is moved to the frontmost or rearmost position. As is known, the sway of the seat and the shock produced during the adjustment movement of the seat gives uncomfortable feeling to a seat occupant.